Solvent Extraction Process For Separating Cobalt And/Or Manganese From Impurities In Leach Solutions

ABSTRACT

A process for the separation of cobalt and/or manganese from impurity elements selected from one or more of calcium and magnesium contained in a leach solution, the process comprising the step of subjecting the leach solution to solvent extraction using an organic solution of a carboxylic acid such as Versatic 10 and a hydroxyoxime such as LIX 63, optionally together with a stabilzer.

The present invention relates to a process for separating cobalt and/ormanganese from calcium and magnesium contained in an aqueous solutionsuch as an aqueous leach solution, and for recovering the cobalt and/ormanganese where desired.

The world mineral industry is experiencing an unprecedented interest inmetal extraction from laterite and sulphide ores throughhydrometallurgical processes. Commonly, the hydrometallurgical processinvolves grinding, leaching and solvent extraction (SX), with recoveryof product via precipitation or reduction processes. The intensity ofthe leaching process (temperature, pressure, bio) depends on the natureof the ore (mineralogy, grade), the distribution of the metal(s) to berecovered and the particle size reduction achieved during grinding.Leach solutions often contain copper, nickel, cobalt and zinc (and/ormanganese) as metals to be recovered (target metals), with calcium,magnesium, iron and aluminium (and manganese if not to be recovered) asimpurity metals to be rejected. Iron (as ferric) and aluminium are oftenremoved by precipitation at low pH (pH 2.5-5.0) prior to SX.

Separations of industrial significance that have proven to beparticularly troublesome include:

-   -   the separation of cobalt (and optionally nickel) from manganese        (and calcium and magnesium), where manganese is to be rejected,        and    -   the separation of manganese (and cobalt and nickel) from calcium        and magnesium, where manganese is to be recovered.

Traditionally, sulphide or hydroxide precipitation followed by re-leachprocesses have been used by industry to effect these separations.

Drawbacks of sulphide precipitation include:

-   -   The separation of manganese from cobalt by sulphide        precipitation is incomplete and causes problems in the        downstream processes.    -   The re-leaching of sulphides needs high temperature and        pressure, indicating high capital and operating costs.    -   The separation of copper and zinc from nickel and cobalt needs        separate processes.

The drawbacks of the hydroxide precipitation process include:

-   -   The use of magnesia as precipitation agent (if used to prevent        gypsum formation) adds cost to the operation.    -   Manganese is partially precipitated.    -   The use of ammoniacal leaching (if used) to separate cobalt from        manganese results in complexity of the flowsheet and causes        serious problems in the downstream processes.    -   Ammonia is expensive and the scrubbing and recovery of ammonia        are difficult.    -   The separation of copper and zinc from nickel and cobalt needs        separate processes.

It is an object of the invention to provide alternative processes for:

-   -   Separating cobalt from calcium and magnesium, and optionally        manganese, especially for solutions deficient in nickel, and    -   Separating manganese from calcium and magnesium, especially for        solutions deficient in cobalt and nickel.

SUMMARY OF THE INVENTION

The present invention is generally based on the development of anorganic solution of a carboxylic acid and a hydroxyoxime which iseffective in shifting the pH isotherms of nickel, cobalt, copper, zinc,magnesium, manganese and calcium in such a way as to enable separationof certain groups of these elements from each other. In particular, theisotherms of the elements copper, zinc, nickel and cobalt are separatedfrom the isotherm of manganese to allow effective separation ofmanganese from these elements. Further, the isotherm of manganese issufficiently separated from the isotherms of calcium and magnesium toallow effective separation of manganese from calcium and magnesium.Thus, when used in combination with certain leach solutions containingappropriate levels of elements, and in appropriate pH conditions, itbecomes possible to separate (and optionally thereafter recover) cobaltand/or manganese from (manganese) calcium and magnesium. Under someconditions, the organic solution of carboxylic acid and hydroxyoxime maybe susceptible to degradation, particularly with respect to thehydroxyoxime component. Accordingly, a stabilizer may advantageously beadded.

According to the present invention there is provided a process for theseparation of cobalt and/or manganese from impurity elements selectedfrom one or more of calcium and magnesium contained in a leach solution,the process comprising the step of subjecting the leach solution tosolvent extraction using an organic solution of a carboxylic acid and ahydroxyoxime. In some situations there is a need to separate cobalt frommanganese only and therefore there is also provided a process for theseparation of cobalt from manganese contained in a leach solution, theprocess comprising the step of subjecting the leach solution to solventextraction using an organic solution of a carboxylic acid and ahydroxyoxime. The organic solution may optionally further comprise astabilizer.

The present invention is a particular example of a more general processfor separating one or more of nickel, cobalt and manganese from theimpurity elements (manganese) calcium and magnesium contained in a leachsolution, which process comprises the steps of subjecting the leachsolution to solvent extraction using a carboxylic acid and ahydroxyoxime. The process of the invention that is the subject of thisapplication is particularly suited to leach solutions containing lowlevels of nickel, since nickel has slow extraction and strippingkinetics in the absence of further additives.

The solvent extraction step described above achieves very goodseparation of cobalt (and/or manganese) present in the leach solutionfrom (manganese,) calcium, magnesium and chloride impurity elementswhich may be present, and good separation of cobalt from manganese ifcobalt is to be recovered and manganese is to be rejected as an impurityelement. If zinc and copper are present, the process comprisesseparation of zinc, copper, cobalt (and/or manganese) from impurityelements selected from one or more of calcium, magnesium (and manganese)contained in a leach solution, the process comprising the step ofsubjecting the leach solution to solvent extraction using an organicsolution comprising a carboxylic acid and a hydroxyoxime. According to apreferred embodiment, the organic solution further comprises astabilizer.

According to one embodiment, the elements cobalt and/or manganeseextracted into the organic phase during solvent extraction are recoveredtherefrom. Where the organic phase of the extraction step containsprimarily cobalt or manganese alone, the recovery step may comprise bulkstripping of the element from the organic phase. The bulk stripping mayoptionally be combined with ion exchange to remove any minor amounts ofimpurity elements, such as zinc, copper and nickel to improve the purityof the recovered elements. Another optional process for improving thepurity of the recovered element is sulphide precipitation. Sulphideprecipitation is more suited to precipitation of any minor amounts ofcopper, zinc, cobalt and nickel present in the manganese recovered fromstripping.

In the situation where the leach solution contains both cobalt andmanganese, and these are both extracted into the organic phase, therecovery step may comprise selective stripping of the organic phase toseparate the manganese from the cobalt. The manganese may thereafter berecovered from the loaded strip liquor, and the cobalt recovered fromthe selectively stripped organic solution by bulk stripping.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in further detail with reference to thefollowing figures which relate to preferred embodiments of theinvention.

FIGS. 1 and 2 are graphs comparing extraction pH isotherms of metalsusing a comparative extraction system (FIG. 1) and the extraction systemof one embodiment of the invention (FIG. 2).

FIG. 3 is a graph showing the extraction kinetics of metals from a leachsolution using the extraction system of one embodiment of the invention.

FIG. 4 is a graph showing the stripping kinetics of metals from a loadedorganic phase from the extraction system of one embodiment of theinvention.

FIG. 5 is a graph comparing stripping kinetics of cobalt using acomparative extraction system and the extraction system of oneembodiment of the invention.

FIGS. 6 and 7 are graphs comparing extraction pH isotherms of metalsusing a comparative extraction system (FIG. 6) and the extraction systemof one embodiment of the invention (FIG. 7).

FIG. 8 is a graph showing the extraction kinetics of manganese from aleach solution using the extraction system of one embodiment of theinvention.

FIG. 9 is a graph showing the stripping kinetics of manganese from aloaded organic phase from the extraction system of a one embodiment ofthe invention.

FIG. 10 a schematic flow chart of the steps of the process of oneembodiment of the invention.

FIG. 11 is a schematic flow chart of the steps of the process of asecond embodiment of the invention.

FIG. 12 is a schematic flow chart of the steps of the process of a thirdembodiment of the invention.

FIG. 13 is a schematic flow chart of the steps of the process of afourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

At the core of the present invention is a synergistic solvent extractionstep which effects extraction of a large proportion of the nickel,cobalt, copper, and zinc into an organic phase (to the extent that theseelements are present), with a large proportion of the calcium,magnesium, and chloride being rejected to the aqueous phase. Dependingon the pH selected, the manganese can report to either the organic phaseor the aqueous phase, as is chosen for a particular leach solution. Thesolvent extraction is conducted with a combination of carboxylic acidand a hydroxyoxime synergist, and optionally a stabilizer.

The hydroxyoxime synergist is capable of increasing the pH gap, ΔpH₅₀,between isotherms for nickel and cobalt and that for manganese, andbetween the isotherm for manganese and those for calcium and magnesium.This results in advantageous selectivity of nickel and cobalt andoptionally manganese, over the impurities (manganese), calcium,magnesium and chloride.

The pH₅₀ value is the pH at which 50% metal extraction is achieved.Thus, ΔpH₅₀ is the difference between the pH₅₀ values for two metals, orthe difference between the pH₅₀ values for the same metal underdifferent extraction conditions.

Carboxylic Acid

In the most preferred embodiment of the invention, the carboxylic acidis 2-methyl, 2-ethyl heptanoicic acid (commercially available asVersatic 10) or a cationic exchange extractant having extractioncharacteristics similar to 2-methyl, 2-ethyl heptanoic acid could beused. Cationic exchange extractants have hydrogen ions which areexchanged with metal ions in the aqueous solution. The term carboxylicacid is used in its broadest sense to refer to any organic carboxylicacid. Carboxylic acids have the formula RCOOH, in which R represents anyoptionally substituted aliphatic or aromatic group, or combinations ofthese groups, including optionally substituted alkyl, alkenyl, alkynyl,aryl, or heteroaryl groups (and combinations thereof). Preferably Rrepresents a relatively bulky group containing at least 4 carbon atoms,and preferably between 4 to 18 carbon atoms. The term “alkyl” usedeither alone or in a compound word such as “optionally substitutedalkyl” or “optionally substituted cycloalkyl” denotes straight chainbranched or mono- or poly-cyclic alkyl, preferably C1-30 alkyl orcycloalkyl, most preferably C4-18 alkyl. Examples of straight chain andbranched alkyl include methyl, ethyl, butyl, isobutyl, tert-butyl,1,2-dimethylpropyl, 1-methylpentyl, 5-methylhexyl, 4,4-dimethylpentyl1,2-dimethylpentyl, 1,3-dimethylpentyl, 1,1,2-trimethylbutyl, nonyl, 1-2- or 3-propylhexyl, decyl, 1-, 2-, 3-, 4-, 5- or 6-ethyloctyl, 1-, 2-,3-, 4- or 5-propyloctyl, 1-, 2- or 3-butylheptyl, 2-hexyl 2-methyloctyland the like. Examples of cyclic alkyl include cyclohexyl, cycloheptyl,cyclooctyl, cyclononyl and cyclodecyl and the like. The alkyl mayoptionally be substituted by any non-deleterious substituent.

In this specification “optionally substituted” means that a group may ormay not be further substituted with one or more groups selected fromalkyl, alkenyl, alkynyl, aryl, halo, haloalkyl, haloalkenyl,haloalkynyl, haloaryl, hydroxy, alkoxy, alkenyloxy, aryloxy, benzyloxy,haloalkoxy, haloalkenyloxy, haloaryloxy, nitro, nitroalkyl,nitroalkenyl, nitroalkynyl, nitroaryl, nitroheterocyclyl, amino,alkylamino, dialkylamino, alkenylamino, alkynylamino, arylamino,diarylamino, benzylamino, dibenzylamino, acyl, alkenylacyl, alkynylacyl,arylacyl, acylamino, diacylamino, acyloxy, alkylsulphonyloxy,arylsulphenyloxy, heterocyclyl, heterocycloxy, heterocyclamino,haloheterocyclyl, alkylsulphenyl, arylsulphenyl, carboalkoxy,carboaryloxy, mercapto, alkylthiom benzylthio, acylthio and the like.

Suitable optional substituents will be chosen on the basis that thecarboxylic acid have the desired extraction characteristics, and thesubstituents do not react with any other component of the mixture underthe given extraction conditions.

Hydroxyoxime

A hydroxyoxime is used as a synergist with the carboxylic acid in thesolvent extraction step. A hydroxyoxime is a compound containing anoxime group and a hydroxy group. Preferably, the groups are in anα-position with respect. to each other. Such α-hydroxyoximes arechelating, whereas oximes are generally non-chelating and thus behavedifferently. The “oxime” functional group contains a carbon to nitrogendouble bond, with the nitrogen atom being attached to an oxygen atom.Accordingly, the term oxime includes within its scope oximes with ahydroxy group attached to the nitrogen atom, and oxime ethers, althoughhydroxime (>C═N—OH) is preferred. The hydroxyoxime may be a C8-C26hydroxyoxime. Preferably, the hydroxyoxime is an aliphatic hydroxyoxime.Preferably, the hydroxyoxime is of the formula:

in which R′ and R″ are each selected from an optionally substituted,straight chain, branched or cyclic alkyl, group containing from 2 to 12carbon atoms. Preferably each of R′ and R″ are unsubstituted alkylgroups, most preferably a heptyl group. An example of such a compound is5,8-diethyl-7-hydroxy-6-dodecanone oxime (the active component of acommercial agent LIX 63). This has the following structure:

Stabilizer

Under some conditions, the reagent mixture of carboxylic acid andhydroxyoxime may be susceptible to degradation, particularly withrespect to the hydroxyoxime component. Accordingly, a suitablestabilizer may advantageously be used to slow any degradation reaction.Degradation may take place via a number of mechanisms, includingoxidation and hydrolysis. Hence the stabilizer is suitably one thatmitigates against oxidation and/or hydrolysis of the hydroxyoxime. Suchstabilsers include, but are not limited to, esters (e.g. TXIB), ethers,ketones, alcohols (e.g. isodecanol, TDA) and alkylphenols (e.g.nonylphenol, dodecylphenol, BHT, Ionol). Preferably the stabilizer is ananti-oxidant. Of these, we have found the alkylphenol anti-oxidants tobe particular useful. The term “alkylphenol” encompasses all alkylderivatives of phenol, and in particular those derivatives with one ormore straight chain, branched or cyclic alkyl substituents. Thealkylphenol 2,6-bis(1,1-dimethylethyl)-4-methyl phenol (commerciallyavailable as BHT and Ionol) or reagents with similar anti-oxidantcharacteristics to 2,6-bis(1,1-dimethylethyl)-4-methyl phenol areparticularly useful.

Leach Solution

The leach solution subjected to the synergistic solvent extraction withthe organic solution of carboxylic acid, hydroxyoxime and optionally astabilizer may be any type of leach solution containing cobalt and/ormanganese, together with impurity elements selected from one or more ofcalcium, magnesium, (manganese) and chloride, optionally together withcopper and zinc. Preferably, the leach solution is one containing littlenickel.

In this respect, the leach solution suitably contains less than 100 ppmnickel, or any other low level that does not warrant recovery foreconomic reasons. Where cobalt is to be recovered, the nickel issuitably present in any amount of less than 50% of that of cobalt (forexample, <100 ppm nickel, >200 ppm cobalt).

According to one embodiment, the leach solution may contain thefollowing levels of elements:

Ni: 0-100 ppm Co: 100 ppm-5 g/L Cu: 0-100 ppm Zn: 0.2-2 g/L Ca: 1ppm-saturated, for instance between 0.5-0.7 g/L Mn: 0.2-50 g/L, or 1-50g/L Mg: 1 ppm-100 g/L, or 2-100 g/L.

The leach solution may for instance be a pregnant leach solutionobtained from the pressure acid leaching of any suitable ore type, suchas a laterite or sulphide ore. It may alternatively be a solution frombio-leach, atmospheric acid leach, oxidative leach, reductive leach,chloride leach or any combination of these leach processes. The stepsinvolved in producing such leach solutions are well known in the art.

The leach solution is preferably a solution that has been subjected to apreliminary iron and/or aluminium precipitation step to precipitate outiron and/or aluminium to leave an aqueous leach solution containing thetarget elements and impurity elements identified above. The leachsolution may alternatively or further have been subjected to one or moreadditional treatment or processing stages.

Synergistic Solvent Extraction Conditions

The solvent extraction step involves contacting an organic solventcontaining the carboxylic acid, hydroxyoxime and optionally stabilizerwith the (aqueous) leach solution. The organic solvent may be anysuitable organic solvent known in the art. Kerosene is the most commonsolvent/diluent used for this purpose due to its low cost andavailability. Shellsol 2046 is one specific example.

The amount of carboxylic acid and hydroxyoxime (and stabilizer) in theorganic solution used in the solvent extraction step will depend on theconcentration of the (nickel), cobalt (and optionally manganese) or bothto be extracted and the A/O (aqueous/organic) flow rate ratio. Theconcentration would typically be in the range of from 0.1 to 2.0 M forcarboxylic acid, with a preferred range of 0.1 to 1.0 M, and 0.05 to 1.0M for hydroxyoxime. The concentration of stabilizer may be in the rangeof from 0 to 0.1 M, typically 0.005 to 0.1 M.

Preferably, the pH of the aqueous phase is maintained in a range from3.5 to 5.0 and more preferably 4.0 to 4.5 in the extraction step ifmanganese is to be rejected. Preferably, the pH of the aqueous phase ismaintained in a range from 5.5 to 7.0 and more preferably 5.8 to 6.3 inthe extraction step if manganese is to be recovered. The temperature ispreferably maintained in the range of from 10° C. to 60° C., morepreferably from 20 to 40° C. Whilst temperatures as low as 10° C. areachievable, a temperature lower than 15° C. results in high viscosity.At temperatures higher than 60° C. there is a risk of increasedevaporation and degradation of the organic phase.

The aqueous to organic ratio (A/O) in the extraction step is mostsuitably 1:1, but may lie in the range from 10:1 to 1:10, and preferably1:5 to 5:1. The aqueous to organic ratio maintained in the scrubbingstep may lie within the range from 1:5 to 1:200, but preferably it is inthe range of 1:5 to 1:20.

The cobalt and/or manganese extracted into the loaded organic phase inthe synergistic solvent extraction can be recovered in downstreamprocessing stages.

Scrubbing

The organic phase from the synergistic extraction step of the inventionis suitably subjected to scrubbing. The scrub solution may suitably be aprocess stream recycled from the process, and is preferably derived froman aqueous stream of a stripping stage (which may be a selectivestripping stage) following the scrubbing stage.

Recovery of Cobalt, Manganese or Both from Scrubbed Organic Solution

There are a number of options envisaged by the applicants for therecovery of cobalt, manganese or both from the scrubbed organicsolution. One example for the situation where both cobalt and manganeseare extracted (i.e. pH of aqueous phase in extraction is 5.5 to 7.0) isset out below. It is noted that other options within the skill andknowledge of those in the art could be used in place of the following,and are within the scope of the present invention. Moreover, differentsteps would be used for different leach solutions containing differentlevels of elements, or when other elements are desired to be recoveredor removed.

Selective Stripping to Separate Cobalt and Manganese

According to one embodiment of the invention, the organic phasecontaining cobalt and manganese is subjected to selective stripping toseparate to a significant extent the cobalt and the manganese. Theselective strip suitably involves contacting the organic phase from thesynergistic extraction with an acidic aqueous solution to yield (a) aloaded strip liquor containing manganese and (b) a selectively strippedorganic solution containing cobalt (and zinc, nickel and copper, if theywere present in the organic phase from the synergistic extraction).

The acidic aqueous solution for the selective strip is suitablysulphuric acid solution, although other aqueous acid solutions known inthe art (such as hydrochloric) may be used. The pH of the acidic aqueoussolution is suitably in the range of about 4.0 to 5.0, depending on thelevel of separation desired. Most preferably, the pH is about 4.5.

The combination of the described synergistic extraction with theselective strip of manganese from cobalt is a very useful combination,enabling the recovery of manganese and cobalt using only one solventextraction circuit (although more than one circuit could be used if sodesired with other process steps).

Other Process Details

The synergistic extraction step of the present invention may be combinedwith different preliminary and following process steps for thedevelopment of processes suitable for the recovery of cobalt and/ornickel when different impurity elements may be present.

It will be well understood to persons skilled in the art of theinvention that scrubbing stages of the type well known in the art may beused for recovering elements even if the scrubbing stages are notspecifically mentioned. The design of the optimum arrangement ofscrubbing stages will depend on the specific aqueous leach solution andthe elements desired to be recovered therefrom (and target percentagerecovery levels).

It is also an advantage of the present invention that cobalt can beseparated from impurities contained in leach solutions withoutintermediate precipitation of the cobalt with other impurity elementsand re-leaching of the precipitate to subsequently enable the removal ofthe impurities. Thus, in a preferred embodiment of the invention, theprocess does not include a precipitation step involving precipitationout of the target elements and re-leaching of the precipitate.

EXAMPLES

The present invention will now be described in further detail withreference to the following examples which demonstrate the underlyingtheory behind the invention, and how the invention is put into practice.

Batch Test Work

Example 1 Extraction pH Isotherms of Metals with Versatic 10/LIX63Synergistic System

This example illustrates that when carboxylic acid 25 Versatic 10 isused as the extractant with no added synergist, the pH isotherms of the“valuable” elements Zn, Ni, and Co are too close to the isotherms of the“impurity” elements Mn, Ca and Mg for effective separation. However whena synergistic system comprising Versatic 10 and hydoxyoxime LIX 63 isused, the isotherms of the “valuable” elements Cu, Zn, Ni, and Co aresufficiently separated from the isotherm of Mn to allow effectiveseparation. Further, the isotherm of Mn is sufficiently separated fromthe isotherms of Ca and Mg to allow effective separation.

The aqueous solution was a synthetic solution to simulate a typicallaterite leach solution containing 3 g/L Ni, 0.3 g/L Co, 0.2 g/L Cu andZn, 2 g/L Mn, 10 g/L Mg and 0.5 g/L Ca.

The metal extraction pH isotherms with the 0.5 M Versatic 10 (carboxylicacid) alone were determined and plotted, as shown in FIG. 1. The metalextraction pH isotherms using the combination of 0.5 M Versatic 10 and0.35 M LIX63 (hydroxyoxime) were also determined and plotted in FIG. 2.Comparison of the two figures reveals that the combination of LIX63 withVersatic 10 resulted in significant synergistic extraction isothermshifts (to lower pH) for nickel, cobalt, copper, zinc, and manganese andantagonistic shifts (to higher pH) for calcium and magnesium. As shownin FIG. 2, with the 0.5 M Versatic 10/0.35 LIX63 system, the ΔpH₅₀values of nickel, cobalt, copper, zinc, manganese and Ca were found tobe 2.8, 3.5, >2.0, 2.0, 1.2 and −0.5 pH units, respectively.

pH₅₀ of metals from pH isotherms in FIGS. 1 and 2 pH₅₀ 0.5 M Versatic10 + Metal 0.5 M Versatic 10 0.35 M LIX 63 ΔpH₅₀ Ni 6.2 3.4 2.8 Co 6.32.8 3.5 Cu 4.1 <2.0 >2.0 Zn 5.7 3.7 2.0 Mn 6.5 5.3 1.2 Ca 7.0 7.5 −0.5

The ΔpH_(50(Mn—Ni)) value for the 0.5 M Versatic 10/0.35 M LIX63 systemwas found to be 1.9 pH units and the ΔpH_(50 (Mn—Co)) value 2.5 pHunits, indicating easy separation of nickel and cobalt from manganese,calcium and magnesium. The ΔpH_(50(Ca—Mn)) value for the 0.5 M Versatic10/0.35 M LIX63 system was found to be 2.2 pH units, indicating easyseparation of manganese from calcium and magnesium.

Example 2 Extraction Kinetics with Versatic 10/LIX63 synergistic system.

This example illustrates that when the synergistic system comprisingVersatic 10 and LIX 63 is used, Cu, Co, Zn and Mn display fastextraction kinetics, while the extraction kinetics for Ni are slow.Hence this system is potentially suitable for Cu, Co, Zn and Mn recoverywhen the leach solution contains little Ni.

Tests were conducted to establish the extraction kinetics of the metalsin the synthetic laterite solution using Versatic 10/LIX63. Theextraction kinetics of copper, cobalt, zinc (and manganese—see Example 6and FIG. 8) were found to be fast and the extraction kinetics of nickelwere found to be relatively slow (FIG. 3). Within 30 seconds, only 55%Ni was extracted and within 2 minutes, only 74%. It is noted that Mn andZn are crowded out as Ni extracts.

Example 3 Stripping Kinetics with Versatic 10/LIX63 Synergistic System

This example illustrates that when the synergistic system comprisingVersatic 10 and LIX 63 is used, Cu, Co, Zn and Mn display fast strippingkinetics, while the stripping kinetics for Ni are slow. Hence thissystem is potentially suitable for Cu, Co, Zn and Mn recovery when theleach solution contains little Ni.

Tests were conducted to determine the stripping kinetics of the metalsfrom the 0.5 M Versatic 10/0.35 M LIX63 system using a strip solutioncontaining 5 g/L Ni and 10 g/L sulphuric acid (FIG. 4). The strippingkinetics of copper, cobalt and zinc were fast. The stripping kinetics ofnickel were slow, with only 18% of the nickel being stripped after 2minutes of mixing.

Example 4 Stripping of Cobalt from LIX63 Alone and Versatic 10/LIX63Systems

This example illustrates that when the synergistic system comprisingVersatic 10 and LIX 63 is used, Co displays fast stripping kinetics,however when LIX 63 alone is used, Co cannot be readily stripped thusmaking LIX 63 alone an unsuitable extractant for Co-containingsolutions.

Cobalt(II) can poison hydroxyoxime reagents such as LIX63. This meansthat once cobalt(II) is extracted by hydroxyoxime reagents (and oxidisesto Co(III)), it cannot be stripped with concentrated acids. Tests wereconducted to see whether the new system results in cobalt poisoning ofthe extractant/synergist.

Parallel tests were conducted with 0.35 M LIX63 alone and 0.5 M Versatic10/0.35 M LIX63 systems by mixing the organic solutions with aqueoussolution containing cobalt (FIG. 5). The organic and aqueous solutionswere left in contact with air bubbling for 76 hours. Thereafter, asulphuric acid solution of 100 g/l sulphuric acid was used to stripcobalt from the loaded organic solution sample. The cobalt strippingefficiency from the 0.35 M LIX63 alone system was only 29.2% after 10minutes stripping. The cobalt stripping efficiency for the 0.5 MVersatic 10/0.35 M LIX63 system was 99.5%. This indicates thatcobalt(II) does not poison the Versatic 10/LIX63 system.

Example 5 Extraction pH Isotherms of Metals with Versatic 10/LIX63System

This example illustrates that when Versatic 10 is used as the extractantwith no added synergist, the pH isotherm of Mn is too close to theisotherms of the “impurity elements” Ca and Mg for effective separation.However when the synergistic system comprising Versatic 10 and LIX 63 isused, the isotherm of Mn is sufficiently separated from the isotherms ofCa and Mg to allow effective separation.

The aqueous solution was a synthetic solution to simulate a typicalwaste laterite leach solution containing 1.46 g/L Mn, 17.6 g/L Mg and0.54 g/L Ca.

The extraction pH isotherms were determined for 0.5 M Versatic 10 aloneand 0.5 M Versatic 10/0.2 M LIX63 systems and shown in FIGS. 6 and 7,respectively. The pH_(50 (Mn)) decreased from 6.9 to 5.6 pH units whilethe positions of isotherms of magnesium and calcium remained virtuallyunchanged. At pH 6.5, the extractions of manganese, calcium andmagnesium were 17.9%, 2.84% (or 46 ppm)and 0.16% (or 82 ppm),respectively, for the Versatic 10 alone system while the extractions ofmanganese, calcium and magnesium were 87.3%, 2.41% (or 39 ppm) and 0.05%(or 26 ppm), respectively, for the Versatic/LIX63 system. This indicatesthat the selectivity of Versatic 10 for manganese over magnesium andcalcium was very greatly improved.

Example 6 Extraction Kinetics with Versatic 10/LIX63 System

This example illustrates that when the synergistic system comprisingVersatic 10 and LIX 63 is used, Mn displays fast extraction kinetics.Hence this system is suitable for Mn recovery.

The extraction kinetics of the metals in the synthetic waste lateriteleach solution using the 0.5 M Versatic 10/0.2 M LIX63 system weredetermined and graphed in FIG. 8. As shown, the extraction kinetics ofmanganese were fast. Within 0.5 minutes, the system almost reachedequilibrium with manganese extraction of 80%.

Example 7 Stripping Kinetics with Versatic 10/LIX63 System

This example illustrates that when the synergistic system comprisingVersatic 10 and LIX 63 is used, Mn displays fast stripping kinetics.Hence this system is suitable for Mn recovery.

The stripping kinetics of the manganese in the loaded 0.5 M Versatic10/0.2 M LIX63 system were determined using a strip solution containing60 g/L Mn and 35 g/L sulphuric acid and graphed in FIG. 9. As shown, thestripping kinetics of manganese were fast. Within 0.5 minutes, thesystem almost reached equilibrium with manganese extraction of 99%.

Process Flowcharts

Example 8 Process for Separation and Recovery of Cobalt and Manganesefrom Leach Solutions

Based on the above findings, a new direct solvent extraction (DSX)process flow sheet was designed. The flow sheet is shown in FIG. 10.

Leach Solution

The leach solution contains manganese and cobalt, as well as theimpurity elements calcium and magnesium, but little or no copper, zincor nickel. A suitable solution composition for this flow sheet maycomprise Co>200 ppm, Mn>1 g/L, Ca<50 g/L (Ca will be<1 g/L in sulphatesolutions), Mg<100 g/L, Cu, Zn and Ni<100 ppm (or of no economic value).It is noted that the flow sheet is not limited to such leach solutions,and the leach solutions may comprise different levels of the givenelements, optionally together with further impurity elements. This leachsolution is one that may have been subjected to preliminaryneutralisation with limestone at pH 4.5-5.0 to precipitate impurityelements Fe (III), Al, Si and Cr.

Synergist Solvent Extraction (SSX EX)

In the synergistic solvent extraction step, an organic solution ofcarboxylic acid (Versatic 10), a hydroxyoxime (LIX 63) and a stabilizer(Ionol) in organic diluent Shellsol 2046 is contacted with the leachsolution at pH 6-6.5 to obtain (a) an aqueous raffinate containingmagnesium and calcium, and (b) a loaded organic solution containingalmost all of the cobalt and manganese, and only minor levels of calciumand magnesium.

Scrubbing (SSX SC)

The organic solution from the extraction step is subjected to scrubbingat pH 5.5-6 using a sulphate solution containing a small amount ofmanganese from the next step of stripping 1, resulting in (a) a scrubbedorganic solution containing cobalt and manganese, and (b) a scrub liquorwhich is recycled to the synergistic solvent extraction step.

Selective Stripping (SSX ST1)

The scrubbed organic solution is subjected to stripping 1 (selectivestrip) using a sulphuric acid solution at pH between 4.0-5.0 resultingin (a) a loaded strip liquor containing manganese, and (b) a strippedorganic solution containing mainly cobalt and only a very small amountof manganese.

The loaded strip liquor is sent to manganese recovery, with one streamreturning to the previous scrubbing stage.

Scrubbing (SSX SC2)

The organic solution from stripping 1 is subjected to scrubbing 2 at apH of 3.5-4.0 using the aqueous strip liquor from a subsequent strippingstage (stripping 2). This step results in (a) a scrubbed organicsolution containing cobalt, and (b) a scrub liquor which is recycled tothe original synergistic solvent extraction stage to maximize cobaltrecovery.

Stripping (SSX ST2)

The scrubbed organic solution is subjected to stripping 2 usingsulphuric acid solution at pH between 2.0-2.5. The cobalt recovered inthis stripping stage is optionally subjected to zinc/copper/nickel ionexchange to enable removal of any zinc, copper and nickel impuritiespresent. The zinc, copper and nickel is disposed of, and the cobalt issent to cobalt recovery by any process known in the art. One example iscobalt precipitation using base or sulphide.

Example 9 Process for Separation and Recovery of Cobalt from LeachSolutions

An alternative solvent extraction process flow sheet was formulated forthe recovery of cobalt from leach solutions 25 containing impurityelements manganese, calcium and magnesium, with little or no copper,zinc or nickel. This flow sheet is shown in FIG. 11. A typical solutioncomposition for which this flow sheet could be applicable comprisesCo>200 ppm, Mn<100 g/L, Ca<100 g/L (Ca will be<1 g/L in sulphatesolutions), Mg<100 g/L, Cu, Zn and Ni<100 ppm (or of no economic value).Of course, variations in this solution composition are possible.

The plant leach solution (PLS) is adjusted to a pH between 4.0-5.0 andsubjected to the synergistic solvent extraction (SSX) described inrelation to Example 8 above. The organic phase contains the cobalt (aswell as zinc, copper and nickel to the extent that these are present)and a minor level of manganese. The aqueous raffinate containsmagnesium, calcium and manganese.

Scrubbing is conducted as described above in relation to Example 8, atpH 3.5-4.5, yielding (a) a scrubbed organic solution containingprincipally cobalt, but also zinc, copper, and nickel in very lowquantities if present at all in the plant leach solution, and (b) ascrub liquor which is recycled to the original synergistic solventextraction stage to maximize cobalt recovery. The organic phase of thescrubbing step contains cobalt, and possibly zinc, nickel and copper,which is then subjected to stripping with sulphuric acid at pH between2.0 and 2.5. The loaded strip liquor is sent to cobalt recovery (withone stream returning to the previous scrubbing stage), optionally viaion exchange, with the organic phase returned to the synergistic solventextraction.

Example 10 Process for Separation and Recovery of Cobalt, Copper andZinc

FIG. 12 details a process flow sheet which is a variation on thatillustrated in FIG. 11, and described in Example 9 above.

The process of FIG. 12 is suitable for recovering copper, cobalt andzinc from leach solutions that contain impurity elements manganese,calcium and magnesium, with little or no nickel. A solution compositionto which this process may suitably be applied contains the following:Cu>500 ppm, Co>200 ppm, Zn>500 ppm, Mn<100 g/L, Ca<100 g/L (Ca will be<1g/L in sulphate solutions), Mg<100 g/L and Ni<100 ppm (or of no economicvalue). Of course, variations in this solution composition are alsoenvisaged.

The plant leach solution is subjected to copper solvent extraction andcopper electrowinning. The leach solution containing reduced levels ofcopper, and all other elements, is then subjected to iron and aluminiumprecipitation (Fe/Al PPT) by neutralising the leach solution withlimestone to a pH of between 4.0-5.0 to precipitate iron and aluminium.The leach solution is then subjected to the synergistic solventextraction, scrubbing and stripping as described in relation to Example9 and FIG. 11 above. As will be appreciated, any copper and zinc stillpresent reports to the phases to which the cobalt reports.

The aqueous phases collected from scrubbing and stripping containcobalt, zinc and minor levels of copper, together with any levels ofnickel which may be present. The aqueous liquor is subjected to zincsolvent extraction to remove zinc therefrom for recovery. Thereafter,the cobalt (and nickel and copper) containing solution is subjected tonickel and copper ion exchange to enable nickel and copper removal anddisposal. Thereafter, the cobalt is recovered.

Example 11 Process for Separation and Recovery of Manganese from LeachSolutions

A new solvent extraction process flow sheet was developed for recoveringmanganese from leach solutions that contain the impurity elementscalcium and magnesium, with little or no copper, zinc, cobalt or nickel.This is set out in FIG. 13. A typical solution composition which may besubjected to this process may comprise Mn>1 g/L; Ca<50 g/L (Ca will be<1g/L in sulphate solutions); Mg<100 g/L; Cu, Zn, Co and Ni<100 ppm (or ofno economic value). Of course, variations in this solution compositionare envisaged.

The leach solution, which may have been subjected to preliminaryprocessing steps, is subjected to synergistic solvent extraction withthe Versatic 10/LIX 63/Ionol synergistic system, with the aqueous phaseadjusted to a pH between 6.0-7.0. The aqueous raffinate contains calciumand magnesium, and the organic phase contains manganese, with minorlevels of calcium of magnesium. The organic phase is subjected toscrubbing using a scrub solution at pH between 6.0-6.5. The scrubsolution is a stream of the manganese sulphate solution generated in asubsequent stripping stage. The organic phase from the scrubbing stagecontaining manganese is sent to stripping, and the aqueous scrub liquoris recycled to the synergistic solvent extraction stage.

Stripping is performed on the organic phase using sulphuric acid at pHbetween 3.0-4.0. The aqueous strip liquor is optionally subjected tosulphide precipitation to remove any copper, zinc, cobalt or nickelimpurities present, and the manganese sent to manganese recovery. Astream of the strip liquor is recycled to the scrubbing stage. Thisprocess is particularly suited for situations where the manganese valueis acceptable, making it desirable to recover the manganese from a leachsolution. If the leach solution contains appreciable levels of cobalt,and other elements having pH isotherms similar to cobalt, then theprocess of Example 8 and FIGS. 10 would be more suited.

Example 12 Effect of Stabilizer (Ionol) on Degradation of Hydroxyoxime(LIX63) in Versatic 10/LIX63 System

This example shows how addition of an anti-oxidant stabilizer (Ionol)slows the rate of degradation of the hydroxyoxime LIX63 in the Versatic10/LIX63 extraction system.

An organic extractant solution (25 mL) containing 0.4 M LIX63 and 0.5 MVersatic 10 in Shellsol D70 diluant was loaded with a synthetic leachsolution (50 mL) containing 0.5 g/L Ca, 9 g/L Na, 24 g/l Mg, 45 g/L Mn,0.2 g/L Co, 1 g/L Zn and 0.15 g/L Cu, at pH 4.5 and left to stand in awater bath at 25° C. Two further (duplicate) systems, each containing 10g/L Ionol were prepared and treated similarly. After 18 days, theorganic solution was sampled and analysed for LIX63 using gaschromatography. The results are shown in the table below. After 18 daysin the Ionol-free system, 5.2% of the LIX63 had been degraded. After 18days in the duplicate systems initially containing 10 g/L Ionol, 0.7%and 1.6% of the LIX63 had been degraded.

TABLE 1 Oxime concentration in the loaded organic solutions as afunction of contact time. LIX63 (%) relative to initial concentrationContact time Versatic 10 + Versatic 10 + Versatic 10 + (days) LIX63LIX63 + Ionol LIX63 + Ionol 0 100.0 100.0 100.0 8 97.0 99.6 99.2 18 94.899.3 98.4

It will be understood to persons skilled in the art of the inventionthat many modifications may be made to the embodiments described withoutdeparting from the spirit and scope of the invention.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention.

1. A process for the separation of cobalt and/or manganese from impurityelements selected from one or more of calcium and magnesium contained ina leach solution, or for separating cobalt from manganese contained in aleach solution, the process comprising the step of subjecting the leachsolution to solvent extraction using an organic solution of a carboxylicacid and an aliphatic hydroxyoxime.
 2. The process of claim 1, whereincobalt poisoning as a result of oxidation of cobalt(II) to cobalt(III)is avoided.
 3. The process of claim 1, wherein the solvent extraction ofthe leach solution with the organic solution produces an organic phaseand an aqueous raffinate, and wherein all of the organic phase issubjected to stripping with an acid solution to strip cobalt from theorganic phase.
 4. The process of claim 3, wherein the stripping with theacid solution is preceded by scrubbing of the organic phase.
 5. Theprocess of claim 3, wherein the stripping with the acid solution ispreceded by a selective stripping stage.
 6. The process of claim 1,wherein the organic solution displays fast extraction kinetics forcopper, cobalt, zinc and manganese.
 7. The process of claim 1, whereinthe organic solution is in contact with the leach solution for a periodof 5 minutes or less.
 8. The process of claim 7, wherein the organicsolution is in contact with the leach solution for a period of 3 minutesor less.
 9. The process of claim 7, wherein the organic solution is incontact with the leach solution for a period of 2 minutes or less. 10.The process of claim 1, wherein the organic solution comprises astabilizer against hydroxyoxime degradation.
 11. The process of claim10, wherein the stabilizer reduces oxidation and/or hydrolysis of thehydroxyoxime.
 12. The process of claim 10, wherein the stabilizer is anantioxidant.
 13. The process of claim 10, wherein the stabilizer is analkylphenol.
 14. The process of claim 1, wherein the leach solutioncontains little nickel.
 15. The process of claim 1, wherein the leachsolution contains cobalt and/or manganese, together with impurityelements selected from one or more of calcium, magnesium, (manganese)and chloride, optionally together with copper and/or zinc.
 16. Theprocess of claim 1, wherein, the leach solution contains the followinglevels of elements: Ni: 0-100 ppm Co: 100 ppm-5 g/L Cu: 0-100 ppm Zn:0.2-2 g/L Ca: 1 ppm-saturated Mn: 0.2-50 g/L Mg: 1 ppm-100 g/L


17. The process of claim 1, wherein the leach solution is a solutionthat has been subjected to a preliminary iron and/or aluminiumprecipitation step to precipitate out iron and/or aluminium to leave anaqueous leach solution containing the target elements and impurityelements.
 18. The process of claim 1, wherein the carboxylic acid is2-methyl, 2-ethyl heptanoic acid or a cationic exchange extractanthaving extraction characteristics similar to 2-methyl, 2-ethyl heptanoicacid.
 19. The process of claim 1, wherein the hydroxyoxime is achelating α-hydroxyoxime.
 20. The process of claim 1, wherein the leachsolution contains cobalt and manganese, and the pH of the aqueous phasein the solvent extraction step is maintained in the range of from 5.5 to7.0 to effect extraction of the cobalt and manganese into the organicphase.
 21. The process of claim 20, wherein the pH of the aqueous phasein the solvent extraction step is maintained in the range of from 5.8 to6.3.
 22. The process of claim 20, wherein the organic phase containingcobalt and manganese is subjected to selective stripping to separate toa significant extent the cobalt from the manganese.
 23. The process ofclaim 22, wherein the selective stripping comprises contacting theorganic phase from the solvent extraction with an acidic aqueoussolution to yield (a) a loaded strip liquor containing manganese and (b)a selectively stripped organic solution containing cobalt.
 24. Theprocess of claim 23, wherein the acidic aqueous solution used in theselective stripping has a pH in the range of 4.0 to 5.0.
 25. The processof claim 1, wherein the leach solution contains cobalt and manganese,and the pH of the aqueous phase in the solvent extraction step ismaintained in the range of from 3.5 to 5.0 to effect extraction ofcobalt into the organic phase and rejection of manganese to the aqueousphase.
 26. The process of claim 23, wherein the cobalt is recovered fromthe organic phase by bulk stripping.
 27. The process of claim 1, whereinthe leach solution comprises zinc and/or copper, the zinc and/or copperare extracted into the organic phase with the cobalt in the solventextraction step, and the zinc and/or copper are separated from thecobalt by ion exchange.
 28. The process of claim 1, wherein the leachsolution comprises manganese and a low level or no cobalt, and themanganese is extracted into the organic phase to effect separation ofmanganese from the impurity elements calcium and/or magnesium.
 29. Theprocess of claim 1, wherein scrubbing is conducted on the organic phaseafter each solvent extraction.
 30. A process for the separation of zinc,copper and cobalt from impurity elements selected from one or more ofmanganese, calcium and magnesium contained in a leach solution, theprocess comprising the step of subjecting the leach solution to solventextraction using an organic solution of a carboxylic acid and analiphatic hydroxyoxime.
 31. The process of claim 30, wherein cobaltpoisoning as a result of oxidation of cobalt(II) to cobalt(III) isavoided.
 32. The process of claim 30, wherein the solvent extraction ofthe leach solution with the organic solution produces an organic phaseand an aqueous raffinate, and wherein all of the organic phase issubjected to stripping with an acid solution to strip cobalt from theorganic solution.
 33. The process of claim 30, wherein the organicsolution displays fast extraction kinetics for copper, cobalt, zinc andmanganese.
 34. A product recovered by the process according claim 1.